But there are some problems. In Russain the verb "to be" is rarely used as an auxiliary verb. E.g., it is not used with adjectives and nouns in the present tense. Он синий (it [is] blue); он учитель (he [is a] teacher).

Я есть and я существую are synonymous. But there also could be a difference between them. Есть sometimes is used to express location. Он есть там. (= Он там находится). But it could be omitted in such phrases. Он там. For me it depends on context.
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